synapse

Examples of synapse in the following topics:

• The Synapse

  • Synapses between axon endings of one neuron and a dendrite is called axodendritic synapse.
  • The neuron conducting impulses towards the synapse is called presynaptic neuron.
  • The neuron transmitting the electrical impulse away from the synapse is called postsynaptic neuron.
  • There are two varieties of synapses: electrical and chemical synapse.
  • The neurons are electrically coupled and transmission across these synapses is very rapid.

• Postsynaptic Potentials and Their Integration at the Synapse

  • Postsynaptic potentials are changes in the membrane potential of the postsynaptic terminal of a chemical synapse.
  • Many postsynaptic membrane receptors at chemical synapses are specialized to open ion channels.
  • At excitatory synapses, neurotransmitter binding depolarizes the postsynaptic membrane.
  • Neurotransmitter binding at inhibitory synapses reduces a postsynaptic neuron's ability to generate an action potential.
  • A single EPSP at one synapse is generally far too small to trigger an action potential in the postsynaptic neuron.

• Mechanics of the Action Potential

  • The synapse is the junction where neurons trade information.
  • The stages of an electrical reaction at a synapse are as follows:
  • Chemical synapses are much more complex than electrical synapses, which makes them slower, but also allows them to generate different results.
  • Electrical synapses are faster than chemical synapses because the receptors do not need to recognize chemical messengers.
  • Long-term changes can be seen in electrical synapses.

• Types of Neurotransmitters by Function

  • Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse.
  • Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse.
  • The coexistence of more than one neurotransmitter in the synapse makes it possible for the cell to exert several influences at the same time.
  • Neurotransmitters are packaged into synaptic vesicles clustered beneath the membrane in the axon terminal on the presynaptic side of a synapse.
  • The next most prevalent is GABA, which is inhibitory at more than 90% of the synapses that do not use glutamate.

• Preganglionic Neurons

  • The preganglionic, or first neuron will begin at the outflow and will cross a synapse at the postganglionic, or second neuron's cell body.
  • The postganglionic neuron will then cross a synapse at the target organ.
  • There are several locations where preganglionic neurons create synapses with their postganglionic neurons:
  • This is the one exception to the two-neuron pathway rule: they create a synapse directly onto the target cell bodies.
  • These are the preganglionic neurons that synapse with the postganglionic neurons in these locations :

• Synaptic Plasticity

  • Synaptic plasticity is the strengthening or weakening of synapses over time in response to increases or decreases in their activity.
  • Plastic change also results from the alteration of the number of receptors located on a synapse.
  • The weakening and pruning of unused synapses trims unimportant connections, leaving only the salient connections strengthened by long-term potentiation.
  • LTP arises when a single synapse is repeatedly stimulated.
  • LTD occurs when few glutamate molecules bind to NMDA receptors at a synapse (due to a low firing rate of the presynaptic neuron).

• Synaptic Transmission

  • In a chemical synapse, the pre and post synaptic membranes are separated by a synaptic cleft, a fluid filled space.
  • Neurotransmission at a chemical synapse begins with the arrival of an action potential at the presynaptic axon terminal.
  • Third, diffusion of the neurotransmitter as it moves away from the synapse.
  • Communication at chemical synapses requires release of neurotransmitters.

• Organization of Motor Neuron Pathways

  • These axons synapse with lower motor neurons in the ventral horns of all levels of the spinal cord.
  • These axons also synapse with lower motor neurons in the ventral horns.
  • Most of them will cross to the contralateral side of the cord (via the anterior white commissure) just before synapsing.
  • The lateral tract contains upper motor neuronal axons that synapse on the dorsal lateral lower motor neurons, which are involved in distal limb control.
  • The anterior corticospinal tract descends ipsilaterally in the anterior column, where the axons emerge and either synapse on ventromedial lower motor neurons in the ventral horn ipsilaterally or descussate at the anterior white commissure where they synapse on ventromedial lower motor neurons contralaterally.

• Neuroplasticity

  • Learning takes place when there is either a change in the internal structure of neurons or a heightened number of synapses between neurons.
  • At birth, there are approximately 2,500 synapses in the cerebral cortex of a human baby.
  • By three years old, the cerebral cortex has about 15,000 synapses.
  • Apoptosis occurs during early childhood and adolescence, after which there is a decrease in the number of synapses.
  • The selection of the pruned neurons follows the "use it or lose it" principle, meaning that synapses that are frequently used have strong connections, while the rarely used synapses are eliminated.

• Neurotransmitters

  • Neurotransmitters are chemicals that transmit signals from a neuron across a synapse to a target cell.
  • Neurotransmitters are chemicals that transmit signals from a neuron to a target cell across a synapse.
  • There are several systems of neurotransmitters found at various synapses in the nervous system.
  • Amino acid neurotransmitters are eliminated from the synapse by reuptake.
  • Neuropeptides are often released at synapses in combination with another neurotransmitter.